Recently, resin materials have been widely used in optical components such as an over-coating agent for optical use, a hard-coating agent, an antireflection film, a spectacle lens, an optical fiber, an optical waveguide, and a hologram because of their good processability and productivity. Furthermore, from the viewpoints of the tendency of a reduction in the size and a reduction in the thickness of optical components and the adjustment of antireflection properties, resin materials having high refractive indices have been desired. In particular, recently, in liquid crystal display elements used in displays of liquid crystal televisions, notebook personal computers, portable video game machines, cellular phones, etc., requirements for a reduction in the size, a high resistance property, and realization of a high brightness have been increasing. To achieve this, it is essential to realize high refractive indices for materials of prism sheets.
From the viewpoint of realization of high refractive indices for materials of prism sheets, in the related art, for example, it is known that a bifunctional acrylate compound having a 9,9-bisphenoxyfluorene skeleton is used as a photopolymerizable monomer (refer to PTL 1 and PTL 2). However, such an acrylate monomer having a 9,9-bisphenoxyfluorene skeleton is a liquid having a high viscosity of several tens of pascal seconds or more at room temperature. Accordingly, when the acrylate monomer is used as a shape-forming material of a prism sheet or the like, it is necessary to dilute the monomer with a large amount of a reactive diluent or the like so that the resulting monomer solution comes to have an appropriate viscosity. Consequently, the refractive index of the resulting cured product decreases.
Compositions that contain N-vinylcarbazole (9-vinylcarbazole) or a derivative thereof are known examples of materials of prism sheets having high refractive indices (refer to PTL 3). However, N-vinylcarbazole has high crystallinity and is difficult to handle. In addition, at present, the refractive indices of cured products obtained by curing any of these compositions are not at a satisfactory level.
As described above, existing high-refractive index polymerizable compounds tend to have high viscosities by themselves or are easily crystallized. As a result, in the case where such compounds are used in practical compositions, it is difficult to sufficiently increase the refractive indices of the resulting cured products.